the blog of LAKE, the Lowndes Area Knowledge Exchange

Citizen dialog for transparent process

Wednesday, 06 March 2013

Sinkholes in Florida, and in Lowndes County, Georgia

The sinkhole that formed under a man's bed and pulled him in has
made a lot of news in Florida, plus another one a few miles away.
But the news seems to neglect why those sinkholes are forming.
Could it be the same reason sinkholes are forming in Lowndes County, Georgia?
And will the Lowndes County Commission do anything about that
before we see news about somebody here falling into a sinkhole?

Jeremy Bush just went to bed when he heard what sounded like a car
hitting the house. Then screams from his brother Jeffrey's bedroom.

"Help me! Help me!"

Someone flipped the lights. Jeremy, 36, threw the door open,
revealing a sight that defied belief: The earth had opened beneath
his brother's bedroom and was swallowing everything in it. The tip
of Jeffrey's mattress was the only thing left, and it was sinking
into a churning sinkhole.

The Tampa Bay Times has a long series on what happened afterwards,
rescue workers who didn't find him, the demolition of the house,
objects found, etc.
They never quite get around to saying why the sinkhole was there.
They first say
(Shelley Rossetter 2 March 2013),

There does not seem to be any immediate danger to other structures
in the neighborhood.

"We feel the conditions are isolated and there is no indication from
the probes that it is anywhere else," McGillivray said.

Experts are still working to determine the exact cause of the
problem.

"My opinion is that this sinkhole has been forming for a while,"
McGillivray said. "It may have been caused by erosion of soil down
into the limestone."

Early Saturday, officials deemed two homes beside the sinkhole as
unsafe also, although they had not been condemned.

Testing at both homes determined they were potentially unstable,
Hillsborough County Fire Rescue spokesman Ronnie Rivera said, and
the residents of those houses were given 20 to 30 minutes to gather
their belongings before being evacuated.

New sinkhole forms 2 miles away

As crews began filling the Seffner sinkhole that claimed the life of
Jeffrey Bush, a second sinkhole was discovered 2 miles northeast of
there Monday. The new sinkhole, about 12 feet around and 5 feet deep
in the center, is beneath a fence that divides the grassy side yards
of two houses along Cedar Tree Lane near the community of Mango
Hills. Hillsborough County spokesman Willie Puz said the two
sinkholes are unrelated. "We even had the geologist that was working
with us on the first sinkhole look at the area and he was able to
determine they're not geologically connected," Puz said. "Sinkholes
are seasonal and this is just possibly a seasonal coincidence." One
of the houses is vacant and for sale. Residents of the other home
were not asked to leave.

A Tampa man died Thursday when a sinkhole suddenly swallowed his
entire bedroom and pulled it deep into the earth. But what exactly
is a sinkhole and how do they happen?

Naturally occurring sinkholes, like the one that killed Jeremy Bush,
are depressions in the earth caused by water erosion of the bedrock
below a land surface. Acidic rainwater seeps through the ground,
reaches soluble bedrock (usually salt, sandstone, or a carbonate
rock such as limestone), dissolves small amounts, and carries the
particles away. Over time (even thousands of years), this process
can enlarge natural pores and cracks in the bedrock, to the point
where large cavities or caves are formed. And with a gaping hole
underground, there's nothing to support the weight of layers of
sediment above—that's when the ground collapses.

But here are a couple of hints:

As The Atlantic
points out,
long periods of drought followed by rain
can also set off collapses. Droughts cause groundwater tables to
drop, and caves that were once filled with water and were therefore
supported by it become weaker. Once rain finally comes, the extra
weight of the soaked-through top layer of earth can cause the cave
to collapse. And beware of tapping into groundwater for agriculture
too, as that can have the same effect as a drought.

Non-naturally occurring sinkholes can form because of water main
breaks, sewer collapses, or even abandoned mines. If there's a
substantial change in the weight of a land surface, such as when
industrial or runoff-storage ponds are created, underground
collapses may also be triggered.

Farmers in Hillsborough and Polk counties pumped nearly 1 billion
gallons of water a day out of the aquifer during the 11-day cold
snap this month, causing 85 reported sinkholes in the region and
about 700 complaints of dried-up or damaged residential wells,
according to figures released Tuesday by the Southwest Florida Water
Management District.

See that word the recent stories avoid?
"Causing".
As in pumping water out of an aquifer can cause sinkholes.
And look what happened just before those recent sinkholes formed.
Kathryn Bursch wrote for WSTP News,
Strawberries survive overnight freeze in Plant City,

Plant City, Florida — After a cold night, workers on Monday
move up and down green rows reaching for globes of red. Strawberry
farmers say their fields around Plant City made it through the dip
in temperatures just fine.

As they have in the past, growers sprayed water throughout the
night, so an icy coating could protect the delicate blooms and
somewhat hardier berries.

What a coincidence!
Once again massive amounts of water pumped out of the aquifer,
and once again sinkholes formed, this time one drawing a man
to his death.
Yeah, sinkholes are seasonal, all right:
they seem to form in the season when lots of water is pumped
out of the aquifer.

What aquifer are they pumping that spray water out of?
The
Floridan Aquifer,
the same system of porous limestone that we drink out of here in
Lowndes County, Georgia.

There is no known connection between the Withlacoochee River south
of the Withlacoochee Wastewater Treatment Plant and the Floridan
Aquifer, where the City of Valdosta withdraws its drinking water for
its citizens. Furthermore, the city's seven wells, which withdraw
the water from the aquifer 300 feet below the surface, are located
near the Valdosta Water Treatment Plant Water Treatment Plant,
adjacent to and within Freedom Park.

Yes, and a Hillsborough County, Florida spokesman said about
multiple recent sinkholes,